1. Field of the Invention
The present invention relates to gate leads for use in thyrister housings and methods for manufacturing the same. More particularly, the present invention relates to gate leads having a permanent closed end located within the thyrister housing.
2. Description of the Prior Art
Gate leads are provided in thyrister housings so as to permit an electrical passageway from outside the thyrister to a semiconductor located within the hermetically sealed ceramic-insulated unit. Erkan et al, U.S. Pat. No. 4,420,869, discloses the common method of manufacturing a thyrister housing having a gate lead. The gate lead is brazed into a hole located on a side of the thyrister housing. Because the gate lead is hollow, the attachment of the lead to the hole in the thyrister housing is maintained and an open end within the thyrister housing which is accessible to soldering with the gate electrode wire from the thyrister semiconductor is provided.
After the gate lead is attached to the thyrister housing, the housing undergoes further cleaning and plating operations. If the gate lead is left open, cleaning and plating solutions may become entrapped within the hollow lead. This can cause corrosion of the gate lead, poor solderability with the gate electrode wire, semiconductor failure, and poor gate current carrying operation. To prevent these occurrences, the gate lead is temporarily plugged or capped at the open end within the thyrister housing before the cleaning and plating of the thyrister housing. However, both plugging and capping the gate lead create problems.
The plugs which are used to close the one end of the gate lead sometimes fall out during the subsequent cleaning and plating operations. This will permit the cleaning and plating solutions to become entrapped within the hollow tube. When a frangible cap is used to close the open end of the gate lead, as disclosed in Erkan et al., the cap must be pierced in order to solder the gate electrode wire within the gate lead. Not only is the frangible cap difficult to pierce, but the conductive cap may flake into the thyrister package after it has been pierced, causing damage, arcing, or a short to occur in the thyrister. Additionally, the pierce operation is time consuming. Moreover, the interior diameter of the gate lead provides a poor solderability surface even under the best of conditions when no cleaning or plating solutions are present. This is due to the difficult nature of plating a blind hole when air is entrapped during the submersion process. Accordingly, there remains a need for a method of manufacturing a thyrister housing gate lead which will effectively prevent the accumulation of entrapped solutions without causing other damage to the thyrister housing, or additional labor during assembly of the semiconductor to the ceramic insulation package.